Worktop mitre joints

[acsimpson]

When making mitre joints on a kitchen surface, should some sort of filler or sealant be used in the joint? If it should be what is likley to be the outcome of not having anything in the joint?

My builders fitted a new kitchen for me and it appears that they have not used anything to seal the joint, although I'm sure the supply list for the kitchen included some sort of joint compound. I began tiling on top of the surface before I realised that they had not sealed the joints so it would now be a huge task to open the joint to put anything into it. Is there anything which I could apply from above or below the joint to seal it without opening it?

Thanks
acs

[plumbbob]

Often, fitters use clear silicone, which would give the joint an invisible seal. This is actually a shortcut because a fitter should use a product called Colorfil, which is available in a huge choice of colours to suit the worktop and is specifically designed to give a solid watertight seal and minimise the joint gap.

I notice some DIY chains stock a limited range, but it should be available from a worktop supplier.

[thedoctor]

See the DIY Projects section on mitering a worktop and there is even a project on worktop joints.

[acsimpson]

Thanks, I found the kitchen worktop project which said that mitre joints were worth attempting as DIY and stopped looking in the projects.

plumbob, unfortunately it doesn't look like my fitters used silicone, glue or anything else to seal the joint. as there is no evidence of it underneath or at the back before I sealed the gap myself. Would adding colour fill (or something else) as mentioned in the mitre joints project to the top do a sufficient job of sealing the gap? If not would there be something else you can recommend to seal the gap (hopefully without disturbing the tiles) or is it now a case of waiting for the inevitable water to seep in and blow the chipboard before trying to get the builders back to fix it?

[plumbbob]

If he did use silicone, it would only be a bead along the top edge and would probably only penetrate a couple of cm's into the top so would not be visible from underneath. Frankly, I would be surprised if he has not used some form of seal because the joint needs to be fixed to prevent it moving and creating a step.

Maybe Colorfil, which is a paste, may not penetrate far enough into the gap to create a big enough seal to be long lasting. Maybe a liquid silicone might do better as the thin liquid may be drawn into the crack, but I have never seen or tried this so can't offer any recommendation.

Maybe you should take this up with the fitter. If the worktop is not sealed to the tiles he may be able to split the joint far enough to fill the gap.

One thing is for sure, if it is not sealed and water gets on it at all, the chipboard will blow, and quickly too.

[savvyJack]

Joining and Sealing.

This can be a bit messy and requires a bit of time but you will never get expansion and water damage to your chipboard laminate tops.
I always think ...... do the job better than anyone else.

Mix up some resin - thats the stuff you use with fibreglass.
Paint the under side of the tops and the joints and the backs that will go against the wall - add 2 or 3 coats.

The resin soaks into the chipboard well, it seals it exceptionally well and it glues joints astronomically well - after all that how yatchs are made but instead of chipboard they use fibreglass.

Best of all any runs mess overkill or spill of resin on your lovely new formica / laminate tops, once dry, scrapes off with as little as a thumb nail - wala
Also - it just keeps getting better, Coloufil and Any other cilicone happily sticks and seals to dry resin better than anything else like the wood chipboard itself.

Best way to waterproof wood - soak it in resin - better than varnish.

Now this little secret will cost a 6 pack of beers.

[chris_on_tour2002]

the manufacturer's advice that usually comes with the worktops is to varnish any 'raw' or cut edges and allow to dry prior to fitting. i always do this using a good quality clear varnish. ronseal floor varnish is my choice as i usually have some kicking around, left over from a job.

soaks in well to the chipboard and offers good protection. the sometimes recommend pva, though as other threads suggest on this site, this is not a good idea as it becomes 'live' again if exposed to moisture.

colorfil/silicone in a thin bead applied prior to the marrying of the worktops gives extra protection and helps to conceal the joint if there happen to be any gaps.

with all methods it is critical to remove excess from the worktop surface immediately (or with the spirit cleaner supplied in the case of colorfil).